I highly recommend Thinkpads. Great support for FreeBSD and Debian right out of the box. I also like that it is painless to upgrade components like RAM, the HDD, at least in the X series models(excluding the carbon, which is an ultrabook). As well as this, you can buy so many different addons for them, you can really tailor it to what you need: 56k modem, WiMAX, 3G, ethernet, PCI-Express, FW, etc. They also take a beating like no other, and while they are not flashy and shiny like every other laptop out there, I have really grown to like the subdued, matte look that they have.

Something else to remember is that Thinkpads are business computers, which means that Redhat has pretty good support for them(see: https://hardware.redhat.com/Lenovo). This is excellent , because that ensures that a lot of Lenovo support makes its way back into the kernel and various other services and applications.